Biomedical subjects

G Rougon

Publications and source records attributed to G Rougon.

At least 19 recordsLinked to original sources

PubMed2000

Negative regulation of central nervous system myelination by polysialylated-neural cell adhesion molecule.

Many factors have been shown to promote myelination, but few have been shown to be inhibitory. Here, we show that polysialylated-neural cell adhesion molecule (PSA-NCAM) can negatively regulate myelin formation. During development, PSA-NCAM is first expressed on all growing fibers; then, axonal expression is down-regulated and myelin deposition occurs only on PSA-NCAM-negative axons. Similarly, in cocultures of oligodendrocytes and neurons, PSA-NCAM expression on axons is initially high, but decreases as myelination proceeds. Importantly, if expression of PSA-NCAM is prematurely decreased in cultures, by either antibody-mediated internalization or enzymatic removal of the PSA moieties with endoneuraminidase N (endo-N), myelination increases 4- to 5-fold. In the optic nerve, premature cleavage of PSA moieties by intravitreous injection of endo-N also induces a transient increase in the number of myelinated internodes, but does not interfere with the onset of myelination. Previously, we showed that axonal electrical activity strongly induced myelination, which could be prevented by tetrodotoxin (TTX), an action potential blocker. Interestingly, removal of PSA moieties does not reverse the inhibition of myelination by TTX. Together, this suggests that myelination is tightly controlled by both positive (electrical activity) and negative (PSA-NCAM expression) regulatory signals.

Animals↗

PubMed2000

The glycosylphosphatidyl inositol-anchored adhesion molecule F3/contactin is required for surface transport of paranodin/contactin-associated protein (caspr).

Paranodin/contactin-associated protein (caspr) is a transmembrane glycoprotein of the neurexin superfamily that is highly enriched in the paranodal regions of myelinated axons. We have investigated the role of its association with F3/contactin, a glycosylphosphatidyl inositol (GPI)-anchored neuronal adhesion molecule of the Ig superfamily. Paranodin was not expressed at the cell surface when transfected alone in CHO or neuroblastoma cells. Cotransfection with F3 resulted in plasma membrane delivery of paranodin, as analyzed by confocal microscopy and cell surface biotinylation. The region that mediates association with paranodin was mapped to the Ig domains of F3 by coimmunoprecipitation experiments. The association of paranodin with F3 allowed its recruitment to Triton X-100-insoluble microdomains. The GPI anchor of F3 was necessary, but not sufficient for surface expression of paranodin. F3-Ig, a form of F3 deleted of the fibronectin type III (FNIII) repeats, although GPI-linked and expressed at the cell surface, was not recovered in the microdomain fraction and was unable to promote cell surface targeting of paranodin. Thus, a cooperative effect between the GPI anchor, the FNIII repeats, and the Ig regions of F3 is required for recruitment of paranodin into lipid rafts and its sorting to the plasma membrane.

Animals↗

PubMed2000

Brain-derived neurotrophic factor restores long-term potentiation in polysialic acid-neural cell adhesion molecule-deficient hippocampus.

The neural cell adhesion molecule (NCAM) and its polysialylated form (PSA-NCAM) contribute to long-term potentiation (LTP) in the CA1 hippocampus. Here we report that the deficient LTP found in slices prepared from NCAM knockout mice and in organotypic slice cultures treated with Endo-N, an enzyme that cleaves the PSA moiety of NCAM, can be rescued by brain-derived neurotrophic factor (BDNF). This effect is not reproduced by nerve growth factor, but can be obtained with high concentrations of NT4/5. The effect of BDNF cannot be accounted for by modifications of N-methyl-D-aspartate receptor-dependent responses or of high-frequency bursts. PSA-NCAM, however, could directly interact with BDNF. Exogenous application of PSA residues or recombinant PSA-NCAM also prevents LTP. Furthermore trkB phosphorylation, and thus BDNF signaling, is reduced in both NCAM knockout mice and Endo-N-treated slice cultures. These results suggest that one action of PSA-NCAM could be to sensitize pyramidal neurons to BDNF, thereby modulating activity-dependent synaptic plasticity.

Animals↗

PubMed2000

Consequences of neural cell adhesion molecule deficiency on cell migration in the rostral migratory stream of the mouse.

In vertebrates, interneurons of the olfactory bulb (OB) are generated postnatally and throughout life at the subventricular zone of the forebrain. The neuronal precursors migrate tangentially through the forebrain using a well defined pathway, the rostral migratory stream (RMS), and a particular mode of migration in a chain-like organization. A severe size reduction of the OB represents the most striking morphological phenotype in neural cell adhesion molecule (NCAM)-deficient mice. This defect has been traced back to a migration deficit of the precursors in the RMS and linked to the lack of the polysialylated form of NCAM. In this study we investigate the morphological alterations and functional properties of the RMS in mice totally devoid of all isoforms of NCAM and polysialic acid (PSA). We show that a morphologically altered, but defined and continuous pathway exists in mutants, and we present in vivo and in vitro evidence that PSA-NCAM in the RMS is not essential for the formation and migration of chains. Instead, we find a massive gliosis associated with the formation of membrane specializations in a heterotypic manner, linking precursors to astrocytes. This finding and the over-representation and defasciculation of axons in the pathway suggest that important interactions between migrating cells and their stationary environment are perturbed in the mutants. Finally, we used transplantation experiments to demonstrate that lack of PSA-NCAM leads to a decrease but not a total blockade of migration and demonstrate that the mutant RMS is functional in transporting normal neuronal precursors to the OB.

Animals↗

PubMed2000

Polysialylated-neural cell adhesion molecule expression in rat pituitary transplantable tumors (spontaneous mammotropic transplantable tumor in Wistar-Furth rats) is related to growth rate and malignancy.

Pituitary adenomas are usually benign neuroendocrine tumors. However, some of those that are histopathologically undistinguishable behave aggressively and metastasize. The polysialylated neural cell adhesion molecule (PSA-NCAM), which is highly expressed during the development of the brain and pituitary, is detected in some neuroendocrine tumors and might be relevant as a prognostic marker in pituitary tumors. In the present study, we have searched for PSA-NCAM expression in four lineages of rat pituitary transplantable tumors (SMtTW). Each lineage, maintained by serial tumor grafts under the kidney capsule and skin, differed in its GH/Prl secretion, growth rate, and malignant behavior. PSA-NCAM expression, detected by immunohistochemistry and Western blotting and quantified by ELISA, varied according to the SMtTW lineage. The benign tumors, SMtTW2, with a low growth rate never expressed PSA-NCAM. Another benign lineage, SMtTW3, with a high growth rate expressed a low amount of PSA-NCAM. The highest PSA-NCAM expression was seen in tumors that grew beneath the skin, invaded the kidney, and metastasized (SMtTW4). Tumors of the SMtTW10 lineage, which behaved as either benign or malignant tumors, were heterogeneous in terms of PSA-NCAM expression. In this rat transplantable pituitary tumor model, PSA-NCAM expression correlated in decreasing order with: (a) invasiveness (P < 0.0001), (b) metastases (P = 0.004), (c) ability to grow under the skin (P = 0.006), and (d) growth rate under the kidney capsule (P < 0.01), but not with hormone secretion (r = 0.207). This model, which is very similar to the human pathology, suggests that PSA-NCAM evaluation is of interest in the diagnosis of malignancy and the prognosis of human pituitary tumors. In addition, the SMtTW tumors could be instrumental in evaluating the effects of new therapeutic agents modulating PSA-NCAM expression.

Animals↗

PubMed2000

Analysis of the L1-deficient mouse phenotype reveals cross-talk between Sema3A and L1 signaling pathways in axonal guidance.

In humans, defects of the corticospinal tract have been attributed to mutations in the gene encoding L1 CAM, a phenotype that is reproduced in L1-deficient mice. Using coculture assays, we report that Sema3A secreted from the ventral spinal cord repels cortical axons from wild-type but not from L1-deficient mice. L1 and neuropilin-1 (NP-1) form a stable complex, and their extracellular domains can directly associate. Thus, L1 is a component of the Sema3A receptor complex, and L1 mutations may disrupt Sema3A signaling in the growth cone, leading to guidance errors. Addition of soluble L1Fc chimeric molecules does not restore Sema3A responsiveness of L1-deficient axons; instead, it converts the repulsion of wild-type axons into an attraction, further supporting a function for L1 in the Sema3A transducing pathways within the growth cone.

Animals↗

PubMed1999

Cell surface expression of polysialic acid on NCAM is a prerequisite for activity-dependent morphological neuronal and glial plasticity.

Polysialic acid (PSA) on the extracellular domain of the neural cell adhesion molecule (NCAM) reduces cell adhesion and is considered an important regulator of cell surface interactions. The hypothalamo-neurohypophysial system (HNS), whose glia, neurons, and synapses undergo striking, reversible morphological changes in response to physiological stimulation, expresses high levels of PSA-NCAM throughout life. Light and electron microscopic immunocytochemistry in normal rats and rats in which cell transport was blocked with colchicine showed that PSA-NCAM is expressed in both HNS neurons and glia, particularly at the level of astrocytic processes that envelop neuronal profiles and can undergo remodeling. Moreover, we confirmed that the overall levels of PSA-NCAM were not greatly altered by stimulation (lactation and chronic salt ingestion). Nevertheless, PSA is essential to morphological plasticity. Using comparative ultrastructural analysis, we found that, after specific enzymatic removal of PSA from NCAM by microinjection of endoneuraminidase close to the hypothalamic magnocellular nuclei in vivo, there was no apparent withdrawal of astrocytic processes nor any increase in synaptic contacts normally induced by lactation and dehydration. Our observations demonstrate, therefore, that expression of PSA on cell surfaces in the adult HNS is indispensable to its capacity for activity-dependent morphological neuronal-glial and synaptic plasticity. The carbohydrate PSA on NCAM can thus be considered a necessary permissive factor to allow neuronal and glial remodeling to occur whenever the proper inductive stimulus intervenes.

Animals↗

PubMed1999

Role for myelin-associated glycoprotein as a functional tenascin-R receptor.

The expression of the immunoglobulin superfamily member myelin-associated glycoprotein (MAG) and the extracellular matrix glycoprotein tenascin-R (TN-R) by oligodendrocytes overlaps in time and space. The two molecules can be neurite outgrowth-inhibitory or -promoting depending on the neuronal cell type and the environment in which they are presented. Here we show that the two molecules directly bind to each other in vitro and that binding sites on TN-R localize to two domains, the fibrinogen domain and the epidermal growth factor-like repeat domain with the N-terminal cysteine-rich stretch. We further show by a functional assay, namely the repulsion of MAG-transfected Chinese hamster ovary cells (CHO) cells from a TN-R substrate, that MAG is part of the signalling pathway of TN-R for cell repulsion. When coated as a uniform substrate, MAG was inhibitory for neurite outgrowth of hippocampal and cerebellar neurons in vitro, when compared to poly-L-lysine, while TN-R enhanced neurite outgrowth. When added to MAG, TN-R neutralized the neurite outgrowth-inhibitory effects of MAG, presumably by blocking the neurite outgrowth-inhibitory domain of MAG.

Animals↗

PubMed1999

Bidirectional signaling between neurons and glial cells via the F3 neuronal adhesion molecule.

F3, a glycosyl-phosphatidylinositol anchored molecule of the immunoglobulin superfamily, is known to influence axonal growth and fasciculation via multiple interactions of its modular immunoglobulin-like domains. We prepared a Fc chimeric molecule (F3IgFc) to identify a) the phenotype of cells bearing F3Ig receptors, b) the glial-expressed molecules interacting with these domains and, c) to characterize in in vitro models the functional impact of the interactions. We observed a strong binding of F3IgFc coated fluorospheres to astrocytes in neural primary cultures and to C6 astrocytoma cells. In agreement, in extracts of developing mouse brain F3IgFc is able to bind tenascin-R, tenascin-C, and isoforms of the proteoglycan-type protein tyrosine phosphatases z/beta. All these molecules are synthetized by glial cells as an indication that F3 participates in neuron-glia interactions. We showed that C6 glia-expressed PTPz/RPTP beta stimulated neurite outgrowth by cortical and cerebellar neurons whereas preclustered F3IgFc specifically modified the distribution and intensity of phosphotyrosine labeling in these glial cells. We also showed that inhibition of tenascin-R interaction with F3 prevented defasciculation of cerebellar explants which normally display a defasciculated outgrowth of neurites on a growth permissive substrate. These results identify F3, RTPz/RPTP beta, and tenascin-R as potential mediators of a reciprocal exchange of information between glia and neurons.

Animals↗

PubMed1999

The PEN5 epitope identifies an oligodendrocyte precursor cell population and pilocytic astrocytomas.

PEN5 is a sulfated polylactosamine carbohydrate epitope first described in a subpopulation of mature natural killer cells. Here we report that it is also expressed in a developmentally regulated fashion in human and rat central nervous systems and that its protein carrier is P-selectin glycoprotein ligand-1 (PSGL-1), a ligand for selectins. In rat neural primary cultures, PEN5 is transiently and selectively expressed by oligodendrocyte precursor cells and marks the transition from proliferative to postmitotic stages. In concordance, in human central nervous system tumors, PEN5 is observed in a subset of oligodendrogliomas and in all pilocytic astrocytomas, a class of tumor of uncertain histogenesis. These data suggest that PEN5-PSGL-1 plays a role in the differentiation of oligodendrocytes and that pilocytic astrocytomas are likely to result from a dysregulation occurring in oligodendrocyte precursor cells at the crucial stage of exit from the cell cycle.

Amino Sugars↗

PubMed1999

N-methyl-D-aspartate receptor blockade affects polysialylated neural cell adhesion molecule expression and synaptic density during striatal development.

Glutamatergic neurons innervate the striatum and form asymmetric synapses with the dendritic spines of striatal efferent neurons. The role of glutamate in striatal development, however, remains largely unknown. Previous studies have shown a dramatic increase in the density of asymmetric synapses in the rat striatum during the third postnatal week, followed by a decrease to adult levels by postnatal day 25. At the same time, the highly polysialylated form of the neural cell adhesion molecule becomes progressively restricted to synaptic regions and then disappears. We have now examined the effects of antagonists of the N-methyl-D-aspartate subtype of glutamatergic receptors on the expression of the polysialylated form of the neural cell adhesion molecule and on synaptic density during this late period of striatal development. Peripheral administration of the N-methyl-D-aspartate receptor antagonist dizocilpine maleate markedly decreased immunoreactivity for the highly polysialylated form of the neural cell adhesion molecule in the dorsolateral striatum and cerebral cortex when drug treatment included postnatal day 20, but not earlier in development. This effect was regionally specific and loss of the polysialylated neural cell adhesion molecule in the striatum was reproduced by the local administration of dizocilpine maleate, DL-2-amino-5-phosphonovalerate or ketamine on postnatal day 20. Quantitative ultrastructural studies of synaptic density with the physical disector method performed after one of the regimens inducing loss of the polysialylated neural cell adhesion molecule (postnatal days 18-20) revealed a 30% decrease in asymmetric synapses in the dorsolateral striatum of treated rats. Symmetric synapses, which presumably do not use glutamate, were not affected. The data indicate that N-methyl-D-aspartate receptors play a role in the late stages of synaptogenesis in the striatum and suggest that a subset of synapses expressing immunoreactivity for the highly polysialylated form of the neural cell adhesion molecule may be dependent on N-methyl-D-aspartate receptor stimulation during a critical period of striatal development.

2-Amino-5-phosphonovalerate↗

PubMed1999

The interaction between F3 immunoglobulin domains and protein tyrosine phosphatases zeta/beta triggers bidirectional signalling between neurons and glial cells.

F3, a mouse glycosyl-phosphatidylinositol anchored molecule of the immunoglobulin superfamily, is known to influence axonal growth and fasciculation via multiple interactions of its modular immunoglobulin-like domains. We prepared an Fc chimeric molecule (F3IgFc) to identify molecules interacting with these domains and characterize the functional impact of the interactions. We affinity-isolated tenascin-C and isoforms of the proteoglycan-type protein tyrosine phosphatases zeta/beta (PTPzeta/RPTPbeta) from extracts of developing mouse brain. We showed that both PTPzeta/RPTPbeta and tenascin-C can bind directly to F3, possibly in an exclusive manner, with the highest affinity for the F3-PTPzeta/RPTPbeta interaction. We observed a strong binding of F3IgFc-coated fluorospheres to astrocytes in neural primary cultures and to C6 astrocytoma cells, and demonstrated, in antibody perturbation experiments, that F3-Ig binding on astrocytes depends on its interaction with PTPzeta/RPTPbeta. We also found by confocal analysis that tenascin-C and PTPzeta/RPTPbeta were colocalized on astrocytes which suggests a complex interplay of interactions between PTPzeta/RPTPbeta, tenascin-C and F3. We showed that the interaction between PTPzeta/RPTPbeta and F3-Ig-like domains can trigger bidirectional signalling. C6 glia-expressed PTPzeta/RPTPbeta stimulated neurite outgrowth by cortical and cerebellar neurons, whereas preclustered F3IgFc specifically modified the distribution of phosphotyrosine labelling in these glial cells. Both effects could be prevented and/or mimicked by anti-F3 and anti-6B4PG antibodies. These results identify F3 and PTPzeta/RPTPbeta as potential mediators of a reciprocal exchange of information between glia and neurons.

Animals↗

PubMed1999

Adrenalectomy increases neurogenesis but not PSA-NCAM expression in aged dentate gyrus.

Ageing is accompanied by a decline in neurogenesis and in polysialylated isoforms of neural cell adhesion molecule (PSA-NCAM) expression within the hippocampus and by elevated basal levels of circulating corticosterone. In a companion study, we demonstrated that suppression of corticosterone by adrenalectomy increased neurogenesis and PSA-NCAM expression in the dentate gyrus of adult rats. Here we show that adrenalectomy increased neurogenesis in this structure in old rats, as measured by the incorporation of 5-bromo-2'-deoxyuridine in neuronal progenitors. This effect was prevented by corticosterone replacement. In contrast, PSA-NCAM expression remained unchanged in comparison with controls. Thus, in the aged brain, stem cells are still present and able to enter the cell cycle. This may point to ways of protecting or treating age-related cognitive impairments.

Adrenal Glands↗

PubMed1999

NrCAM, cerebellar granule cell receptor for the neuronal adhesion molecule F3, displays an actin-dependent mobility in growth cones.

The neuronal adhesion glycoprotein F3 is a multifunctional molecule of the immunoglobulin superfamily that displays heterophilic binding activities. In the present study, NrCAM was identified as the functional receptor mediating the inhibitory effect of F3 on axonal elongation from cerebellar granule cells. F3Fc-conjugated microspheres binding to neuronal growth cones resulted from heterophilic interaction with NrCAM but not with L1. Time-lapse video-microscopy indicated that F3Fc beads bind at the leading edge and move retrogradely to reach the base of the growth cone within a lapse of 30-60 seconds. Such velocity (5.7 microm/minute) is consistent with a coupling between F3 receptors and the retrograde flow of actin filaments. When actin filaments were disrupted by cytochalasin B, the F3Fc beads remained immobile at the leading edge. The retrograde mobility appeared to be dependent on NrCAM clustering since it was induced upon binding with cross-linked but not dimeric F3Fc chimera. These data indicate that F3 may control growth cone motility by modulating the linkage of its receptor, NrCAM, to the cytoskeleton. They provide further insights into the mechanisms by which GPI-anchored adhesion molecules may exert an inhibitory effect on axonal elongation.

Actins↗

PubMed1998

Expression of L1 and PSA during sprouting and regeneration in the adult hippocampal formation.

The objective of the present study was to evaluate the expression of polysialic acid (PSA) and the cell adhesion molecule L1 during axonal regeneration and sprouting after injury to the adult rat brain. All animals received a complete lesion of the fimbria-fornix (FF). Grafts of nerve growth factor (NGF)- or beta-galactosidase (betaGal)-producing fibroblasts were placed in the FF lesion cavity and induced septohippocampal cholinergic regeneration or sympathetic tyrosine hydroxylase (TH)-positive sprouting, respectively. Cholinergic regeneration was evaluated from 2 to 8 weeks following grafting of NGF-producing fibroblasts in the FF lesion cavity. In the graft area, choline acetyltransferase (ChAT)-positive fibers expressed L1 and PSA. Once cholinergic axons reached the hippocampal formation (HF), they no longer expressed L1 or PSA. Eight weeks after a lesion of the FF and transplantation of betaGal-producing fibroblasts, TH-positive fibers sprouted in the denervated HF and expressed L1 but not PSA. At the zone of reactive gliosis, PSA but not L1 expression was increased following a lesion of the FF and transplantation of NGF- or betaGal-producing fibroblasts. In animals that received a graft of NGF-producing fibroblasts in the FF lesion cavity, numerous ChAT-positive axons were observed along these areas rich in PSA and reactive astrocytes. Taken together, these results suggest that the expression of PSA and L1 is upregulated on regenerating cholinergic axons during axonal elongation and downregulated upon target innervation. In contrast, TH-positive fibers that sprout in the denervated HF express and maintain their expression of L1. Finally, the expression of PSA in the area of reactive gliosis may contribute to a permissive environment for axonal regrowth.

Age Factors↗

PubMed1998

A functional interaction between the neuronal adhesion molecules TAG-1 and F3 modulates neurite outgrowth and fasciculation of cerebellar granule cells.

F3 and TAG-1 are two closely related adhesion glycoproteins of the Ig superfamily that are both expressed by the axons of cerebellar granule cells. In an in vitro system in which cerebellar granule cells were cultured on monolayers of transfected Chinese hamster ovary (CHO) cells, we show that F3 and TAG-1 interact functionally. F3 transfectants have been shown to inhibit outgrowth and induce fasciculation of granule cell neurites. By contrast TAG-1 transfectants have no effect on these events. However, when TAG-1 is coexpressed with F3, the inhibitory effect of F3 is blocked. Two possible mechanisms may account for this functional interaction: (1) either TAG-1 and F3 compete for the same neuronal receptor, and in favor of this we observed that binding sites for microspheres conjugated with F3 and TAG-1 are colocalized on the granule cell growth cones, (2) or alternatively, F3 and TAG-1 associate in a multimolecular complex after their binding to independent receptors. Extensive co-clustering of F3 with TAG-1 can in fact be achieved by anti-TAG-1 antibody-mediated cross-linking in double-transfected CHO cells. Moreover, F3 coimmunoprecipitates with TAG-1 in Triton X-100-insoluble microdomains purified from newborn brain. These data strongly suggest that F3 and TAG-1 may associate under physiological conditions to modulate neurite outgrowth and fasciculation of the cerebellar granule cells.

Animals↗

PubMed1998

Growth and fate of PSA-NCAM+ precursors of the postnatal brain.

Oligodendrocyte-type 2 astrocyte (O-2A) lineage cells are derived from multipotential stem cells of the developing CNS. Precursors of O-2A progenitors express the polysialylated (PSA) form of the neural cell adhesion molecule (NCAM) and are detected in neonatal rat brain glial cultures. It is unclear how such PSA-NCAM+ "pre-progenitors" are related to neural stem cells and whether they still have the potential to differentiate along several neural lineages. Here we isolated PSA-NCAM+ pre-progenitor cells from glial cultures by immunopanning and found that most of these cells expressed nestin and PDGF-receptor-alpha but not O-2A antigens. PSA-NCAM+ cells synthesized transcripts for fibroblast growth factor (FGF) receptors 1, 2, and 3 and responded to FGF2 by survival and proliferation, growing into large clusters resembling neural spheres. FGF2-induced proliferation of PSA-NCAM+ pre-progenitors was significantly enhanced by thyroid hormone (T3), which on its own did not increase cell survival or mitosis. After adhesion and withdrawal of the mitogen, spheres generated mostly oligodendrocytes and astrocytes but very rarely neurons. PSA-NCAM immunopanned cells grown in epidermal growth factor (EGF) also adopted a mostly glial fate after differentiation. In contrast, PSA-NCAM-negative cells and striatal neonatal stem cells, grown in EGF or FGF2, generated the three CNS cell types. Like neural stem cells, PSA-negative cells generated more oligodendrocytes and fewer neurons when expanded in FGF2 and T3. Thus emergence of PSA-NCAM at the surface of neonatal brain precursors coincides with their restriction to a glial fate. T3 modulates these events by enhancing PSA-NCAM+ pre-progenitor growth in FGF2 and favoring an oligodendrocyte fate.

Animals↗

PubMed1998

Regulated expression of the cell adhesion glycoprotein F3 in adult hypothalamic magnocellular neurons.

F3, a glycoprotein of the immunoglobulin superfamily implicated in axonal growth, occurs in oxytocin (OT)-secreting and vasopressin (AVP)-secreting neurons of the adult hypothalamo-neurohypophysial system (HNS) whose axons undergo morphological changes in response to stimulation. Immunocytochemistry and immunoblot analysis showed that during basal conditions of HNS secretion, there are higher levels of this glycosylphosphatidyl inositol-anchored protein in the neurohypophysis, where their axons terminate, than in the hypothalamic nuclei containing their somata. Physiological stimulation (lactation, osmotic challenge) reversed this pattern and resulted in upregulation of F3 expression, paralleling that of OT and AVP under these conditions. In situ hybridization revealed that F3 expression in the hypothalamus is restricted to its magnocellular neurons and demonstrated a more than threefold increase in F3 mRNA levels in response to stimulation. Confocal and electron microscopy localized F3 in secretory granules in all neuronal compartments, a localization confirmed by detection of F3 immunoreactivity in granule-enriched fractions obtained by sucrose density gradient fractionation of rat neurohypophyses. F3 was not visible on any cell surface in the magnocellular nuclei. In contrast, in the neurohypophysis, it was present not only in secretory granules but also on the surface of axon terminals and glia and in extracellular spaces. Taken together, our observations reveal that the cell adhesion glycoprotein F3 is colocalized with neurohypophysial peptides in secretory granules. It follows, therefore, the regulated pathway of secretion in HNS neurons to be released by exocytosis at their axon terminals in the neurohypophysis, where it may intervene in activity-dependent structural axonal plasticity.

Animals↗